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How does the F-22 Raptor radar reflector work?
The F-22 Raptor (and other stealth aircraft) can be made more visible to radar by using radar reflectors, or in other words, radar cross section (RCS) enhancers. In the comments section of this answer to a question posted on Aviation Stack Exchange it was speculated, that the RCS enhancer used in F-22s is empty, sparking further wondering whether this was in fact possible.
So the question here stands: how can such a small device improve the visibility of a stealth aircraft sufficiently to make it a clear radar target?
The RCS enhancer on F-22 seems to be less than half a gallon (4 litres) in volume.

The F-22 RCS enhancers size and shape (to some extent), as well as this source for example, suggest it is a Luneburg lens. The Luneburg lens is a device that reflects electromagnetic waves very efficiently back to the source, making it possible for a small device to appear as a big target on a receiver placed at same position as the transmitter (for example a radar).
According to  Wikipedia:

Luneburg lenses are normally layered structures of discrete concentric shells, each of a different refractive index. These shells form a stepped refractive index profile that differs slightly from Luneburg's solution. This kind of lens is usually employed for microwave frequencies, especially to construct efficient microwave antennas and radar calibration standards.

This site further elaborates on the Luneburg lens:

The Luneberg lens is a passive radar augmentation device used to increase the radar reflectivity of a target without the use of additional energy The lens reflector is a sphere in shape, usually composed of concentric dielectric shells. By the proper selection of dielectric constants for each shell, radar energy incident on one of the faces of the lens is focused at a point on the rear surface of the lens. The rear conductive surface reflects radar energy back to the source.
Principal of Operation:
(1) Basically the Luneberg lens is made of concentric shell of polystyrene with varying reflective indices (dielectric constants) from 1 to 2, the highest refractive index being the innermost shell.
(2) A ray passing through the various concentric shell will bend towards normal and then focus at a point. If a metal reflector is placed around the focal point, the ray gets reflected and retraces the same path. This is the principal of Luneberg Lenses
(3) In order to have smooth bending of the ray theoretically, many concentric shells are required. In practice, a few concentric shell are used.
(4)The radar cross section augmentation of the lens is given by the formula( 4∏3R4/4λ )
The RCS is inversely proportional to the squire of the wave length and directly proportional to the 4th power of the radius."

[sic]  Note: the correct spelling is Luneburg, after Rudolph Lüneburg
To act as a Luneburg lens, the device cannot be empty. To properly "bend" the incoming and outgoing waves, the sphere must hold some kind of inner refractive structure to make it function properly as a radar reflector over meaningful distances. A single concave spherical layer of reflective material will not achieve this.
It should be noted that the RCS enhancer on F-22 is not spherical in form, but a cylinder with rounded ends. The principle of Luneburg lens could still be applied to the device. And as always, having the inter of net as source, it is totally possible the aforementioned device operates on a different principle. Operating principles of many of the systems on F-22 are not exactly public for obvious reasons... Please feel free to overthrow this answer if better knowledge is available.

What does this do that a transponder doesn't?

It is a passive system that works with any primary radar, when for transponder to work, you need secondary radar system (as I'm sure you know). It is fail safe and hides stealth capabilities of F-22 (stealth stealth ). F-22 did not originally have transponder capability, so this thingy was especially handy then.

Actually I am more familiar with threat radars that ATC.  But I'm still not understanding why an F-22 might want to deny controllers the useful information available via transponder, but allow them a small raw "blip".  What am I missing?

@MichaelHall -- the thing about having a passive reflector is that it will still work when the electrons go on strike :)

So how do you deactivate it?

@MichaelHall: You land at a suitably equipped base and have the ground crew uninstall it.

@MichaelHall I think the main (if not only) reason for using RCS enhancer is to hide the stealthiness of F-22. Not even the U.S. is safe from intelligence and espionage. With proper equipment would very easy to evaluate steath properties of the acft unless something was used to set them off. Flying non operational missions close to enemy makes this even more important. One good example was seen during evaluation flights of F-35 in Finland: they carried radar reflectors, I bet Russia had plenty of their ECM and other relating stuff at full use during F-35 flights in Finnish airspace.

Much of it comes down to the fact that the F-22 has such low radar visibility that you don't need a very large visible surface to drastically increase its visibility.
The number I've seen thrown around for the effective radar cross section of an F-22 is 0.0001 square meters.
With the radar cross section starting out that tiny, a reflector doesn't have to be very big to increase it by a large percentage. A 2 inch diameter piece of steel (or aluminum or other radar reflective material) would be large enough to drastically increase the visible radar cross-section.
The problem with that is that it depends heavily on the angle. It's a bit like if I'm shining a flash light around a room, and you're holding up a hand-sized mirror. If you hold the mirror at just the right angle, the light reflects back to me. But if the angle's wrong, the light reflects off some other direction (that's a lot of how low visibility designs get their low cross section to start with).
So consider instead holding up mirrored ball from a '70s disco. Now no matter what direction you hold it, as soon as I shine my light toward you, I'm pretty much guaranteed to see a reflection. And if two or three people are shining lights toward you from different directions, they'll still all see reflections.
The RCS enhancer is basically that disco ball, but tuned for radar instead of visible light. Oh, and because of how it works, it's more like half a disco ball instead of a whole one, so it covers roughly 180 degree field instead of a full 360 degrees.
But the size still comes back to the fact that the visibility starts out extremely low, so the reflector doesn't need to be terribly huge to increase it a lot. And after decades of work on radar, it doesn't have to be very big for radar to pick it up quite easily.

0.0001m^2 is 1cm^2 (plausible for F-22) , so shoud the RCS-E under F-22 work on the disco ball -principle, it would either be able to multiply RCS about 10 fold in very narrow angle window, or say, about double it in a wider range of discrete angle windows. You must have noticed a disco ball does not shine uniformly, it sparkles as it spins (moves) so getting a constant uniform reflections from a spherical multi-faceted reflector is not possible. The distances in radar surveillance are considerable, so I bet it is preferrable to get a strong reflection, just for the sake of safety alone.


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May a VFR-only pilot without high-performance or complex endorsements be the safety pilot for an IFR currency flight?
For an IFR currency flight in a high-performance and/or complex airplane where the pilot flying has all the appropriate ratings and endorsements to be PIC, does another pilot with strictly a private ASEL certificate meet the legal requirements to be the safety pilot?
If so, I would assume the entire flight must be conducted in VMC. What other constraints or restrictions apply in such a scenario?
If permissible, how may the safety pilot log the flight so as to count toward future ratings and so on?

Some good relevant reading: http://www.aopa.org/News-and-Video/All-News/2013/August/1/Pilot-Counsel-Safety-pilot

First, can a pilot without an HP endorsement act as safety pilot in an HP aircraft? Since 14 CFR 91.109 only requires a safety pilot to have category and class ratings, there's no need to have any additional endorsements.
That's confirmed in this FAA legal interpretation:

there is no regulatory requirement that a safety pilot have a
  high performance endorsement to act as safety pilot

The same document says that safety pilots are "encouraged to be thoroughly familiar and current in the aircraft that is used" - which is great advice - but that's it.
As for the flight conditions (IMC/VMC) and rules (IFR/VFR), I'm not sure what you're asking. Is either pilot IFR current? If not, then the flight can only be VFR. This question might be relevant.

What about a complex endorsement for the safety pilot? I assume the PIC is current, instrument rated, endorsed out the wazoo. To simplify, the safety pilot has 42 hours total time and just passed a PVT-ASEL checkride yesterday.

just rated. and that includes a type rating if required

61.31 requires these endorsements for the legal pilot in command only.  If the safety pilot is not the legal pilot in command the endorsements are not required.
The only requirement is for the safety pilot to be appropriately rated and have a current medical.  See 91.109

I understand the rule, but don't understand the intent.   How can the safety pilot be "safe" if he/she is not IFR rated, doesn't know what to look for, and cannot take over if needed?

@abelenky IF the actual PIC is the flying pilot (not the safety pilot), then the safety pilot's sole "job" is to be there to watch for conflicting traffic since the actual PIC is unable to do so when under the hood.  He doesn't need to know the IFR rules, have an instrument rating, etc. because he isn't the PIC and isn't responsible for the safe outcome of the flight.  The actual PIC is.

Nowhere in 91.109 does it say the safety pilot needs a current medical.  Please correct me if I am missing it.

@RyanMortison The safety pilot is a required crew member and as such needs a medical.  The language in 91.109(c)(3)(ii) requires a pilot with at least a private pilot license.  To exercise the privileges of such certificate a third class medical is required.  See 61.23.

@wbeard52 You can exercise private and PIC  privileges with BasicMed, you don't need a third class medical. On the other hand, acting as a required crewmember (like a non-PIC safety pilot) does require a medical. See this question.

I agree.  BasicMed is a medical certificate.

Sure, but "See 91.109" does not explain that.  I am simply point out that you've referenced 91.109 as your source for that statement, but 91.109 says no such thing.  I am, however, not saying that isn't true in general (although I'm not 100% convinced it is) just that it is not in 91.109 as you're citing.

@Pondlife good link, does the FAA's answer, "BasicMed cannot be exercised by safety pilots who are not acting as PIC but are required
crewmembers." not imply that A) a safety pilot could potentially NOT be acting as PIC, and B) that if they are a "required crewmember", then BasicMed IS NOT satisfactory?  PIC or not, I would agree that the safety pilot is a required crewmember if the other pilot flies simulated IMC meaning a medical is required, and it can't be BasicMed.

@RyanMortensen I'm not sure what you're asking, which I'm sure is my fault :-) The FAA's FAQ seems to cover this?

@pondlife I think maybe I'm agreeing with you.

@RyanMortensen That's what I thought but I wasn't sure :-)

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How do the various DUATS differ?
In terms of technical capability, what are the comparative advantages and disadvantages between the following?

CSC DUATS from Computer Sciences Corporation
DTC DUAT from Data Transformation Corporation
www.1800wxbrief.com from Lockheed-Martin

Interesting question. Do you use DUATS directly? I have a CSC account but I use it from Garmin Pilot so I never see DUATS itself.  I don't know if using DTC would give me a different data set within GP, though.

When I first started training there was actually a pretty substantial difference between DUAT and DUATS (one was a really archaic wrapper around a dial-in modem system, complete with -formatted text everywhere, and the other had nice things like graphical weather) - the gap has really closed a lot these days.

Both DUAT (DTC) and DUATS (CSC) provide the same information. They are functionally equivalent.
You also left one out: Lockheed-Martin operates a web-based briefing service at
https://www.1800wxbrief.com/ .
Which you prefer to use for interactive access is largely an aesthetic consideration - as a pilot you can sign up for an account on each of these services, so the usual advice is to sign up for all of them and use the one you like better (personally I used to prefer DTC's DUAT interface, but the direct (1800wxbrief.com) system is a now my preference for web-based briefings when I'm not using ForeFlight).

From a non-interactive standpoint, CSC DUATS has an API that can be used by other programs (like ForeFlight) to receive weather/NOTAMs/etc. and to file flight plans. This can be advantageous, however Lockheed-Martin has recently (2013) implemented an XML-based API that lets application developers directly communicate with the automated flight service system, and it is likely that this will be the preferred way to handle this sort of thing as time goes on.

Thanks for the excellent answer as usual. I broadened the scope of the question to include 1800wxbrief.com.

Technically, there shouldn't be a difference between these providers. Both providers were tested by FAA to confirm that their major functions meet FAA's standards and requirements. Although, each service service has slightly different features and presents the information in different ways. It is more a matter of personal preference and likeliness, and one's comfortableness.
Both these services use FAA database to obtain weather and aeronautical information and to file, amend, and cancel flight plans. They provide direct access to weather information via a National Airspace System Data Interchange Network II (NADIN-II) interface to the Weather Message Switching Center Replacement (WMSCR) System.
In addition the to above mentioned services, many people like FltPlan. It is also approved by FAA. FltPlan is is funded by advertising and provides a better format and information than government subsidized programs.
Aviation Weather Center is another option (Aviation Digital Data Service) which is funded by FAA. It is an excellent source for icing conditions. It does not meet all requirements of FAA.
The bottom line is that whichever service tells you all the information and you are comfortable with it not to miss any critical information is the most suitable for you. However, many people plan their flights in one service and then double check it with others to make sure that they haven't missed anything.

I didn't know Harris was the prime on that. laughs (I worked as an intern for the software development firm that was subcontracted to do much of the WMSCR software.)

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How does ATC deal with apparent compass errors when giving vectors?
Pilots should strive to fly precisely, but we sometimes reach task saturation.
When ATC gives a heading, receives the correct readback, but observes a 10- to 15-degree difference between the actual and intended tracks, does the specialist incorporate this difference into future vectors? Do approach and traffic separation vectors generally have a healthy margins of error?
How does apparent compass deviation or directional gyro precession factor into vectors that ATC issues?

It's the pilots responsibility to verify and correct the gyro drift, but if a controller sees you on the wrong heading they will issue it again or give you a correction.  I believe it's the pilots responsibility to factor that in our correct the gyro drift for future vectors.

Wind drift is another factor affecting the track seen on radar scopes, and not one that is due to pilot error. Apart from comparison to other aircraft tracks at a comparable altitude, location, and speed, a controller may not be able to tell the difference between wind drift and pilot error.

This question is a partial duplicate of this one and this one.

When ATC gives a heading, receives the correct readback, but observes a 10- to 15-degree difference between the actual and intended tracks, does the specialist incorporate this difference into future vectors?

Sometimes. The controller issues headings but observes ground track.  If the wind is causing drift, the controller will compensate for it when she provides vectors.  Sometimes, if an aircraft is suitably equipped, a controller will ask for a wind report in order to better judge the winds at altitude.

Do approach and traffic separation vectors generally have a healthy margins of error?

Yep.  See here.

How does apparent compass deviation or directional gyro precession factor into vectors that ATC issues?

It's up to the pilot, not the controller, to correct for compass deviation (since only the pilot can see the compass correction card inside the aircraft) and gyro precession (since only the pilot can turn the little knob to reset the gyro).


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What would happen to the rudder on an A320 if both FAC systems failed?
What would happen to the rudder of an A320 if both Flight Augmentation Computer (FAC) systems completely failed during mid-flight? Would the auto pilot immediately pass control back to the pilots or if they  failed would that be it? Would it be impossible for the cockpit to communicate with the mechanisms which control the rudder or is manual operation possible in an A320?
Also, I know this maybe a more difficult/impossible questions but what would cause the malfunction of one of the FAC computers? Are there any likely scenarios or previous cases?

This is mostly a guess, but I think the rudder trim wheels would still work. Also the only way I could imagine both FAC's failing is if they power to them was switched off. Avionics software and hardware is incredibly reliable.

@raptortech97: According to the diagrams here, rudder trim is purely electronic.

@HenningMakholm ah, you're right. I must have been thinking of the elevator.

The A320 has a mechanical link from the rudder pedals to the hydraulic rudder actuators. Computer-generated rudder commands for yaw damping and turn coordination are added to the mechanical signal from the rudder pedals, but in the event of a two-sided computer failure the rudder can still be controlled.
The elevator trim wheels are also mechanically connected, so rudimentary control of the aircraft remains even in the event of a total electronic failure, as long as there's hydraulic power.

@Federico: Hm, I may be misreading the diagrams, but to me it looked like the only thing that actually grips the rudder surface are three hydraulic actuators. If the hydraulic pressure goes away, what good is it that the pedals are mechanically connected to their controlling valves?

I went to check and you're correct, also the THS requires hydraulic power, I remembered otherwise.

@Federico: The hydraulic systems will still work for some time if they stop being powered because some power is accumulated in the reservoirs. They won't work if they are all punctured and there is no backup for that.

Thanks everyone this is all really helpful, so just to clarify even if both FAC systems fail, or direct power is pulled so they can no longer operate, manual rudder control is still possible as long as the hydraulic pumps connected to the rudder remain operational? Thanks again

@user7077: Yes.

The Flight Augmentation (FAC) performs the following functions:

Yaw damper  Rudder travel limiting
Monitoring of the flight envelope and computation of maneuvering speed
Yaw autopilot order
Bite fuction of the AFS

The trim actuator, the yaw damper servoactuators and the travel limitation unit are normally controlled by the flight Augmentation Computer (FAC 1) and FAC 2 being in standby.
The rudders are controlled either mechanically from the pedals or electrically when the auto pilot is engaged. Therefore if both FACs fail, the rudder control remains unaffected. However the autopilot is no longer available.

Only the Rudder has a mechanical link which remains functionnal enough even with electrical commands failure. Landing with it together with engine control only has been tried during certifications.

this is partially incorrect. The mechanical backup includes the THS trimwheel.


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Do turbine engines on multi-engine aircraft rotate in opposite directions to offset torque?
I'm not an aviator, I guess I'd call myself an enthusiast. I'm also a physics nut. I've always wondered about this but I equally worried my question posed to a commercial airline crew would land me in the Homeland Security Suites.
On helicopters, torque along the vertical axis is countered by a smaller tail rotor (or a twin main rotor rotating in the opposite direction).
My question is whether the turbines/fans of multi-engine jet aircraft rotate in the same direction. I.e., do both the port engine and the starboard engine rotate uniformly clockwise or counterclockwise?
It seems like if that were the case then maintenance might be easier but it would create some instability along the longitudinal axis of the airframe due to torque and moment arms.
Follow up: I guess, then, that single engine propeller aircraft utilize trim presets to compensate for the longitudinal torque generated by their propeller–correct?

Torque is less of a problem due to the effective roll damping of a wing, but gyro effects and prop wash are important. Gyro effects first became an issue with rotary engines in WW I. A rotary engine has its crankshaft fixed to the airplane, and both the cylinder block and the propeller rotate. This gives better cooling at low speed and produces a flywheel effect, so the engine runs more smoothly. But when you yaw, the gyro effect pitches the aircraft up or down, so any precise maneuvering becomes very hard.
With the increasing engine power in 1916 and 1917, this effect became so severe that geared engines were developed where the cylinders rotate in one direction and the propeller in the opposite direction. As a consequence, the propeller had only half the RPM in air as it had with the cylinder block. This gave great propeller efficiency, but also big propeller diameters, so airplanes with those engines needed a high landing gear. Below is a picture of a Roland D XVI with a Siemens & Halske III counter-rotating rotary engine from 1918 (source). This was an excellent fighter aircraft for its time with almost no gyro coupling.

Today, high power propeller aircraft tend to use identical engines but left- and right-handed gearboxes so the propellers run in both directions. This is less due to gyro effects and mostly to produce benign stall characteristics. The prop wash of a propeller increases the local angle of attack on the wing on one side and decreases it on the other side, so the wing will stall first on the side with bigger angle of attack. If this side is always to the right of the propellers, the aircraft will roll right in a stall. In the WW II period, a number of multi-engined aircraft used left-hand and right-hand turning engines in order to have the prop wash cancel out.
With jets, the rotating inertias are much smaller because the diameters are smaller. But there is one exception: The Bristol-Siddeley Pegasus engine of the Kestrel, Harrier and AV-8B jump jets needs to have the low pressure spool run in opposite direction of the high pressure spool to balance its gyro effects. If that would not be the case, a yawing motion would produce a pitching motion, and vice versa. When you sit on a jet, the thrust of which is equivalent to your weight, tilting this jet fore or aft only slightly will produce a quick shift of your location, so any maneuvering in hover will become extremely hard.

USMC AV-8B Harrier in hover (picture source)
Some modern turbofans also have counter-rotating low and high pressure spools. While most two-spool engines reduce bearing losses by having both spools rotate in the same direction, some modern engines can avoid one stator stage by having their spools rotate in opposite direction. This lowers engine length and mass.

Nice bit of historical perspective and extra kudos for discussing the vtol craft.

Engines on airliners turn the same direction. The torque isn't as much an issue on jets as it is on props.
A lot of multiengine prop planes have propellers that turn in opposite directions. In turbine engines this can be done in a gearbox to allow the same engine to be used on both sides.
Some turbine engines, such as the PT6, have two turbines turning in opposite directions, but the propeller friction produces additional torque in one direction.
Single engine planes sometimes have the engine mounted at a slight angle to reduce the effect of the propwash (and maybe torque?). The propwash causes imbalance at low speed and high power when the descending blade tends to push air down over the wing on that side, and and vice versa for the ascending blade.
Immediately after takeoff, the rudder of a single engine plane is normally depressed, to some extent, to make up for the uneven torque and propwash. This may be done manually, with trim settings, or both.
At higher speeds, the effect of the propeller torque is not as noticeable because the wings are held "more tightly" by the airflow.

Cheers, thanks for the extended explanation. "The torque isn't as much an issue on jets as it is on props"... is that due to the greater mass (in the case of an airliner) being acted on by the torque?

Nice answer! I like, not even to correct you but maybe make it some simpler at one point. At the end you wrote that the effect isn't noticeable,  or less noticable at higher speeds. This is simply because the aircraft is in it's designed optimum speed range where it is build and trimmed for. See for example addionaly attached fixed trim tabs at the rudder - these changes are normaly made during flight testing when they notice that thei design isn't as well as they expected it to be ;)

I think it's a matter of rotational air friction rather than mass. Mass would only matter during acceleration. The prop blades have a larger radius (per plane size), so more torque from the air for a given horsepower. Also, behind the compressor fans of a jet there are vanes to straighten out the airflow longitudinally, causing the air to exit the jet with less rotation. This would reduce the torque from the air.

Good point, @falk.

Falk, there is another factor at work here.  When speeds are low, the prop plane has a high deck angle (angle between the direction of flight and the floor of the plane.  In other words, it is flying nose high.  When this is true, the descending blade has a significantly higher angle of attack than does the ascending blade.  Therefore the descending blade produces more thrust.  This tends to turn the nose of the plane to the left (in most planes) requiring right rudder to maintain straight flight.  As speed increases and the deck angle decreases, both sides of the prop pull evenly continued

so that pressure on the rudder pedal may be relaxed.

Let's give a short and snappy answer regarding jets: it's all about efficiency.
If a part of an engine is damaged then the engine will most likely be replaced and repaired while the aircraft is flying with another engine. An engine turning clockwise and an engine turning counterclockwise are two different engines. Let's do some simple economics now: is it more efficient to have only one extra engine you can use regardless of which engine failed or if you need an extra engine for each side? Clearly the most economical maintenance solution is to ensure both jets, regardless of the side of the airframe they attach to, are identical and thus interchangeable.
Speaking as someone who's not a scientist, the torque effect at jet engines indeed is negligible.
How about props? The biggest factor affecting props is that an ascending blade  delivers less lift (in forward direction) than the descending blade. If you now chose two engines both turning in the same direction and attach these to the wings of an aircraft, one side has the descending blade outboard and on the other side it will be inboard - now you have a critical engine. If the engine where the descending blade is inboard (critical engine) fails, it creates a greater yaw than if the other engine fails. Now you need to evaluate if safety and structural design allow you to have two engines turning in the same direction.

Ugh. Can you revisit your second paragraph? Do you really mean to imply a jet will be replace "while flying?"

Well, this would be an incredibly good maintenance job, but probably not manageable. I think everybody can understand what I wanted to say, but if you have some better words to describe it, please feel free to edit my answe.

Turbine engines of the same family, all rotate in the same direction. Imagine having to build a turbine engine that rotated opposite. The cost would be over the top. The airlines would be inventorying duplicate spares for the engines.


text:
Where is the airspace not covered by primary Radar?
Most ATC in the world rely primarily on secondary radar to know where planes are. This requires that the transponder on the plane works correctly.
This means that maintenance and deployment of primary radar is no longer a primary concern for airspace regulation. It becomes at best a secondary backup system before they need to pull out the flight progress strips and airways charts.
Where are the spots that is not covered by primary radar? I understand that some military ships have primary radar and can act as a mobile radar during operations.

bonus points for a nice chart of Malaysia in relation to that missing plane.

My therory is that MH370 was a reapet in history from hijack of a pilot on egypt air 990, after one of the two pilots went to the lavatory a second replacement pilot steps into the cabin and then the plane viers of course and flys for another 7 hours

There are a few spots not covered by primary radar. Here are a few I can think off:

Afghanistan, not really what you'd expect from flying between Europe and South East Asia. I was told though by the pilots that the Americans were keeping an eye on us. I'd imagine there are a few holes in the CIS countries as well.

Multiple areas in Africa, but this is improving I believe. There's a post on PPrune. Apparently known as the 'dark continent' for spotty coverage and consistency. South Africa has good coverage, and I'd guess the same for much of northern Africa as well.

A few remote areas in South America, then again, improving.

Oceans are not covered.

Determining factors are population density, aircraft density and economic development.

As more you Malaysia map, if there's a radar at Kota Bharu [KBR] airport, here's the map assuming a range of 200 Nm for the radar. It should in theory be well within reach.

(source: gcmap.com)
And an extended version:
SGN Ho Chi Minh City (Saigon) [Tan Son Nhat Intl], VN
KUA Kuantan [Sultan Abmad Shah Airport (Pedang Geroda Airport)], Pahang, MY
KUL Kuala Lumpur (Sepang) [Intl], Selangor, MY
KBR     Kota Bharu [Sultan Ismail Petra], Kelantan, MY

(source: gcmap.com)
Just for the interested, here's a map showing Japanese military radar, just to get an idea of coverage in a country full of people and planes.

Maps from http://www.gcmap.com/

A lot of airspace is not covered with primary radar, at least not for ATC purposes.
Most airspace above seas and oceans are not covered by ATC primary radars. ATC relies mainly on secondary radar for surveillance, primary radar is used mainly for airspace infringement protection and airport surface surveillance. Over oceans and remote areas procedural control is used, without any surveillance.
Most primary radars used for long range surveillance in ATC are operating in the L-Band. L-Band signals do not follow the curvature of the earth very well; at low altitude the range is limited because the aircraft are below the horizon. At higher altitudes the range is up to about 250NM, but only when the radar is operated at very high power, which is costly both in design and electricity bill. In many cases it is not needed to operate at long range.
Radar is also shielded by terrain; in mountainous areas it is difficult to cover the valleys. In Europe, and I believe also in the US, high altitudes are well covered by primary radar, at low altitude there are many gaps.
A lower band (HF - UHF) radar can be used to look over the horizon (OTH radar). This type of radars is used for Air Defence purposes. The resolution is very poor compared to radars used for ATC but it serves well as an early warning system for incoming enemy aircraft and missiles. This type of radar requires huge antenna arrays, over a kilometre long and they consume enormous amounts of power.
The effective range is typically about 3000 km. For example Australia has the Jindalee Operation Radar Network, that can see past Jakarta, Indonesia.

JORN coverage
In case of the missing Malaysian MH370, and the latest suspicions that the aircraft ended up West of Perth, I wonder whether the flight was tracked by the OTH Air Defence radars of Australia.

In relation to missing flight MH370, and the radar coverage of that region, please see the link to the Department of Civil Aviation Malyasia's primary and secondary (SSR) radar services in the region.
http://aip.dca.gov.my/aip%20pdf/ENR/ENR%201/ENR%201.6/Enr1_6.pdf
The first page lists all the Primary and Secondary (SSR) civil/military radar services and then page 10 graphically represents the 200NM SSR ranges of each station.
So to determine how much of the map is covered by primary radar only, you can match the names of the stations on the map with the table on page 1, and use the 200NM area as a guide to determine the primary radar reach of each station.
As an example, the BBC website shows how flight MH370 changed course with this graphic:

If we look at the radar coverage map again, we can see that this means the flight passed through the primary radar station coverage of Kota Bharu, listed as 1.1.4(g).
Hope this helps, and I hope all the people are found safe.

There are large gaps in radar coverage in the Gulf of Mexico.  The FAA sponsored a study that looked into receiving ADS-B reports from aircraft in the surveillance gap and reformatting them to look like radar reports from a fake radar sensor in the Gulf so they could be ingested by their existing air traffic control software systems.

Adding a reference would improve this answer.


text:
Do landing strips suffer from potholes or rutting?
In companion to the other question asking about wheel tire tracks.
Planes come down and stop with a significant amount of force which I would expect to cause either rutting or potholes.
Are runways susceptible to ruts and potholes?
And do these cause significant issues for landing planes?

Yes, they do, and it can indeed pose significant problems for aircraft.
Asphalt runways are susceptible to ruts (because asphalt isn't really solid - it's solid aggregate suspended in an extremely viscous liquid). The friction (heat) from landings partially melts the asphalt, and the weight of the aircraft slowly pushes it outward away from the landing gear, creating ruts. (There are also other ways you can cause ruts on asphalt runways, such as landing overweight aircraft on them on extremely hot days).
Concrete runways are theoretically less susceptible to rutting, but have their own maintenance challenges.

Runways can also develop potholes, cracks, and spalling - just like a road surface.
Because a pothole can cause loss of control on landing (if the landing gear falls into it and blows a tire or yanks the plane to one side), or serious damage to aircraft engines (if some of the material ejected from the pothole gets pulled into a jet engine's intake or kicked up by a propeller) airports take a lot of effort to prevent (and where necessary, repair) this kind of damage, and routinely inspect their runways.
Airports also do a lot of preventative maintenance on their runways, sealing open cracks and joints in the pavement material to prevent water from infiltrating under the runway and causing potholes (see the image below - click to enlarge).

The FAA has a lot of information on runway pavement design, which I will affectionately call "More than anyone ever wanted to know about runway design, and never asked!"

Your first two links are both dead.


text:
Why do aircraft leave the cruising altitude long before landing just to circle?
Often flights will leave the cruising altitude long before the actual landing. They will go down to a couple of thousand feet and stay at that altitude and  circle for quite a while in waiting loops before it's actually their turn to land. It can be seen basically all the time at Heathrow Airport (LHR). But also for example in Munich Airport (MUC), where flights often come far down over the city and then make wide turns towards the airport.
So I'm wondering: if it's already clear ahead of time (and I'm sure mostly it is) that it's not their time to land yet, why not circle at higher altitudes? Often those waiting loops occur over dense populations and thus create quite some noise on the ground.

A couple of thousand feet? The lowest level for Heathrow's stacks is 7000ft, and aircraft will enter higher than that. See Heathrow arrival paths

It’s still an altitude at which you can clearly hear the planes on the ground

Interesting link though!

"creating quite some noise" Username checks out :)

@silent Noise intensity falls off with the square of distance. An aircraft at 7000ft is already about one tenth as noisy as one at 'a couple of thousand feet'. Having lived near Biggin Hill for many years I can tell you that the traffic noise from the M25 was far more intrusive than the passing jets.

@ReddHerring: Biggin Hill is closed to commercial traffic, which could have something to do with the low aircraft noise levels there.

@sean We're not talking about traffic visiting the airfield, but traffic using the Biggin hold while en route to Heathrow.

@ReddHerring While it's true the intensity falls of rapidly, that's exactly a good reason to hold higher than they currently do. Unfortunately there's a whole lot of reasons why it's also a good idea to hold lower and noise pollution often isn't a primary concern. The M25 being noisier in a certain area doesn't make air traffic less of a problem all of a sudden. Even though LHR has it sorted better than some other major airports in that regard.

Since you specifically talk about LHR and flying low over the city, I think you might be confusing holding stacks with landing approaches.  Planes typically want to land into the wind and the prevailing winds in the UK are from the west or southwest. That means that planes at Heathrow usually want to land from the east, which means that a plane coming from the west will fly across London, then do a 180-degree turn over central or east London at fairly low altitude before flying west to land.

Fair enough. The other example of MUC might be actually more what my question is about. There holding stacks - at least like in LHR - are much less common. But still planes will run long approaches on a mostly steady, low altitude

As far as noise is concerned, they are also slowly washing off speed during this descent, which is somewhat of a powered glide. ATC can also interleave traffic on approach with less complexity. It can also depend upon the origin of the traffic.

The cruising altitude is a way to reduce drag while flying at high speeds. There's no point in flying fast while circling - it's not going to make you reach your destination faster, and you're just wasting fuel.

Airports can accept landing aircraft at a (mostly) fixed, constant rate. However, inbound aircraft arrive at different times and rates based on weather and other factors, regardless of the schedules. This means, at times, aircraft will be coming in faster than the airport can accept them, from many different directions. And airplanes can't just stop mid-air to wait their turn.
The answer is to put aircraft in a "holding pattern", which is a racetrack (not circle) shape that repeatedly passes over the same fixed point, to delay them. When you do this at multiple altitudes, it becomes a "holding stack".
Arriving aircraft are directed into the top of the stack, 1000ft above the previous one. Aircraft at the bottom of the stack are released at a fixed rate to continue toward the airport, and all the aircraft above them are shifted down 1000ft.
The depth of the stack will vary depending on numerous factors, but at congested airports like Heathrow, every arriving plane is pretty much guaranteed to do at least a few turns in holding. And yes, this can mean a lot of noise on the ground for those who live under the stacks. That is the price of airports not being able to expand to increase their arrival rate.

Thank you for your answer. However my question was more about why the holding pattern occurs on rather low altitudes. Why need often need to wait in line (or in stacks...) is clear to me

@silent It depends how close the stack is to the airport. In general, the bottom of the stack will be how high airplanes should be if the stack isn't in use. The standard descent angle is 3° (about 1000ft per 1.5nmi), so if the bottom of the Heathrow stacks is at 7000ft, I'd expect them to be about 10nmi from the airport.

As an aside to the hold explanations furnished above: to save on fuel, an airliner will reduce power to commence descent at a distance from the airport which will place it at either 1) its anticipated hold altitude, or 2) the landing pattern entry altitude, subject to ATC's instructions, upon arrival in the vicinity of the airport.
While at reduced power, the pilot will trim the aircraft for the optimum power-on glide angle that lets him or her make best use of the plane's gravitational potential energy during the descent and approach, and thereby minimize fuel burn during that phase of the flight. The pilot will adjust this to conform to ATC instructions by adding power or deploying spoilers, flaps, or gear as required.

Useful information, but the question seems to be about holding patterns.

understand, will edit.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the purpose of the small fins on top of the wing surface of Boeing aircraft?
I've noticed on most Boeing aircraft that there are small fins on the upper surface of many of their wings. They are about one inch high and maybe two inches long (it's difficult to judge size from inside the passenger cabin without any reference) and spaced about a foot apart.
On the 737 there are eight of them spaced about a third of the way from the wing's root to its tip. On the 757 and 777 they are spaced out to almost the wing's tip, and I can't see them on any pictures of the 747's wing.
Here's a picture of them on the 737's wing:

What purpose does these serve?
The only thing I can think of is that they somehow discourage span-wise airflow, but they seem too small and short to accomplish much. The stall fences I've found in pictures via Google are all much larger and extend around and under the leading edge.
OTOH, a diagram I found here suggests that they are placed at just about the place where the airflow turns span-wise.

They must serve some purpose.

They are called vortex generators, and their function is to create a small vortex which re-energizes the boundary layer. Here is a better picture which also shows that their leading edge is swept like that of a delta wing:

Vortex generators on a T-45 (picture source)
In essence, they are small wings which each create their own delta wing vortex. This vortex mixes fast-moving air from outside the boundary layer with the air close to the wing surface, which has been slowed down by friction. This helps

at low speed to delay flow separation at high angle of attack
at high speed to avoid an oscillation of the shock position when the supersonic pocket of flow over the wing is decelerated in a shock which can cause local flow separation.

The diagram in your question about "Leading edge vortexing" is very misleading. Air does not flow like shown by those arrows.
An airfoil initially accelerates the air which flows over its top surface and decelerates it again over its rear part. On swept wings, this acceleration-deceleration only affects the orthogonal speed component, so the speed component in span direction remains unaffected. This is the reason for the higher Mach capability of swept wings, but also causes the air to flow first inwards and then outwards while transversing the wing's upper surface. The diagram shows no such inward flow, which is wrong.
In addition, friction decelerates the air flowing around a body, such that a layer of decelerated air surrounds each surface of an airplane. The thickness of this boundary layer increases with flow length, and on a swept wing this friction will initially mostly affect the orthogonal flow component. At around mid chord you will find air which has been decelerated mostly in its orthogonal speed component (since this component was so high over the forward part) and now will be subject to more deceleration of the orthogonal component, so that only the spanwise component will be left over the rear part of the boundary layer. Now this boundary layer will only flow off in span direction, such that a massive increase of slow, low-energy air will be collecting towards the tips.
A thick boundary layer will cause early flow separation, so when the angle of attack is increased, the flow at the tips of a backward swept wing will separate first. This will cause lift loss, and since the tips are also the rearward part of the wing, will shift the aerodynamic center forward. This in turn will make the aircraft pitch up, which aggravates the stall condition. If the separation happens asymmetrically, the aircraft will roll in addition to pitching up.
Both vortex generators and wing fences help to reduce this cross flow and delay flow separation on the outer wing at high angle of attack. Vortex generators also help to prevent boundary layer separation past a shock at transsonic speeds when placed close to the leading edge, something a wing fence is incapable of. Therefore, they are more helpful and have displaced wing fences on many swept wings.

So, if I understand correctly, their particular placement on the inboard section of the 737's wing helps keep the root from stalling before the tip; is this correct? (Or is should this be its own question?)

@BillOer: No, the ones near the root help to fix the shock location in cruise. In a stall it is desirable to have the root stall before the tip. Unfortunately, once the question is in the "hot questions" section, people come over from all places and upvote the answer with the many pictures, regardless of the content. On the inner wing of the 737, the vortex generators are for high speed flight, not for stalling.

They are vortex generators, used to delay flow separation. These vortex generators are usually attached near the leading edge of the wing and create small vortices, that prevent flow separation at high angles of attack.

Image from microaero.com
During normal flight, the airflow is accelerated over the wing, producing lift. At this point, the airflow is attached to the upper surface. However, the airflow loses its adherence and separates from the wing, aircraft performance can suffer in the form of increased drag, loss of lift and higher fuel consumption. The vortex generators act by 'mixing' the air in boundary layer with free stream air (through the vortices), thereby preventing the flow separation.
A number of Boeing aircraft use them. The following figure shows the vortex generators (32 no.s) used in 777 and 777 PIP.

Vortex generators in 777 and 777 PIP. Image from Boeing AERO qtr_03 | 09
For swept wing aircraft, there is also a spanwise flow along the wing from the center toward the tips, in addition to the flow in direction of flight. This causes the boundary layer to thicken towards the tips, making them more susceptible to stalling than the wing root. As the ailerons are near the tips, this will make the ailerons lose control and create a pitch up moment (as it is usually aft of cg), which further exacerbates the problem, causing the whole wing to stall (due to increased angle of attack).
For preventing spanwise flow, wing fences are used, which are different from these. For example, the MiG-17 had prominent wing fences.

"MiG-17F Top View" by Robert Lawton - Robert Lawton. Licensed under CC BY-SA 2.5 via Commons.
The function of both vortex generators and wing fences are the same (to prevent flow separation at high angles of attack); however, they go about it in different ways - vortex generators by creating vortices that prevent the boundary layer from separating, and wing fences by preventing cross flow by creating a boundary condition through the fences.

Interesting explanation and beatiful images but why Airbus does not use this solution to reach the same result? It uses a different solution?

It's not a matter of "Airbus doesn't use them" -- the A300 has vortex generators (other Airbus planes may as well, I'm not sure).  There's always trade-offs involved with stuff like this, some times it makes more sense to use vortex generators and some times it makes more sense to design the wing such that they aren't needed, or said another way that the benefits of having them aren't enough to justify the cost.  And on top of that, "costs" could be added complexity in the design, added cost in manufacturing, or added ongoing fuel consumption or maintenance.


text:
Airbus towing: is it necessary to switch on the Y HYD pump?
So, somehow our operations came up with a new requirement: if one of our A320 or A340 is being towed, we are supposed to switch on the Y ELEC pump (if the engines are off). This shall prevent inadvertent retraction of the nose gear caused by the towing force.
Is this even mechanically possible for A320/A340 airplanes? I highly doubt it...

That just doesn’t sound right.

... isn’t that what landing gear pins are for?

I wonder if that HYD pressure has any contribution to the braking system other than preventing accidentally retraction of the NLG.

Please read fully the answer to understand the matter.
Please be careful, with respect to the 320 it depends on the aircraft generation, as I remember if not all, some A320 landing gears are green operated. Nevertheless, by switching on the yellow electrical pump, the green circuit will be pressurized via the PTU, thus preventing the towing force to cause inadvertent retraction of the nose gear.
This is just an explanation, not a procedure to be followed.

A source for this information would be helpful.

A320 hydraulics. https://www.quora.com/What-hydraulic-systems-has-A320


text:
What is the best way to learn about the EASA regulation structure?
I want to increase my awareness of EASA regulations and be able to better understand the differences between EASA baseline regs and operator regs.
However, I frequentl get lost on the EASA website trying to navigate the regulations. It seems I always only find the amendments but not the latest base docs. I am interested in, e.g., flight duty regulations, low wx procedures. What is the best way to get to grips with EASA?

It is funny that almost a year later, no one even commented on this.


text:
Why is Airbus' FCOM structure so different from EASA's recommended OM-B structure?
aicraft operators are allowed to publish their own operations manuals part "B" and in the past, have done so. I nrecent years, many operators revert back to "plain old vanilla" FCOM as published by Airbus.
However, the Airbus FCOM is structured as follows:

FCOM

General
Systems
Procedures

Abnormal
Normal
Special Operations

Limitations
Temporary Abnormal Behaviours
Performance

MEL
CDL

Whereas the EASA OM-B recommended structure is as follows:

0 General
1 Limitations
2 Normal Procedures
3 Abnormal and Emergency Procedures
4 Performance
5 Flight Planning
6 Mass and Balance
7 Loading
8 CDL
9 MEL
10 Survival Equipment
11 Emer Evacuation
12 Systems

Why do we have these differences? What are the rationales between these different structures? Why do Airbus and EASA not sit together and fix this?

Note the document OM part B, introduced by EASA OPS 1.045, is the equivalent of FAA AC 120-71. Both are related to operating procedures developed by operators, and aimed to standardize procedures among different aircraft of an operator. Thus not only EASA and Airbus might sit together, but also other manufacturers, other aviation authorities and operators.


text:
What is the minimum possible number of hours required to carry passengers?
Not factoring learning curve, personal safety minimums, and pilot proficiency, what is the absolute minimum flight time that must be logged in order to carry a passenger in a piston engine aircraft in the United States?
I'm am looking for an answer for the airplane category. Not gliders or ultralights.

I believe the answer, at least in the US is 20 hours of flight time, plus however long a checkride takes. A sport pilot can carry a single passenger and the minimum requirements are outlined in 14 CFR §61.313:

If you are applying for a sport pilot certificate with [...]
Airplane category and single-engine land or sea class privileges,
Then you must log at least [...]
20 hours of flight time, including at least 15 hours of flight training from an authorized instructor in a single-engine airplane and at least 5 hours of solo flight training in the areas of operation listed in §61.311,

If a sport pilot applicant logged exactly 20 hours, got signed off, and then passed their checkride on the first attempt... they would be able to fly passengers as soon as they completed the checkride. That means, realistically, probably 21 to 21.5 hours.

My CFI had a student whose checkride concluded with the engine running on the ramp until the Hobbs ticked over to 35 hours (Part 141 PPL), so that padding may not be required.

Zero, if you bring along a flight instructor :-)
You fly the plane, the flight instructor keeps you safe and legal, and your passenger sits in the back seat.

Isn't that the CFI carrying the passenger, then? :)

Top of my head:
11.5 hours can get you an Ultralight license. Max 1 passenger and 750kg total weight
46.5 hours will get you a PPL. You can carry up to 19 passengers, beyond that you need a type-rating on the airplane, so you add a few more hours (depends on airplane)
202 hours will get you a CPL. Same as above, but now you are allowed to charge them for the flight.

As @egid pointed out, you skipped LSA pilot in your list.  By his answer it does look like a new pilot can take a passenger in about 21 hours.


text:
May a pilot legally fly an ILS approach to ILS minimums with an inoperative Attitude Indicator without declaring an emergency?
A seasoned pilot told me the other day that if the vacuum system fails while on final approach leaving the Attitude Indicator (AI) inop, the pilot must use localizer minimums even with both glideslope and localizer needles functioning normally.
Is this accurate, or did I misunderstand?

If possible, check with that guy for the source of info.

As far as I understand it, a vacuum failure in IMC is an emergency. I think the bigger issue is if you have to go missed approach, you can only use the LOC/glideslope until you hit decision altitude then you need to rely on other instruments to get you to your alternate.

For the record, the asker changed the question after I answered, specifying that not declaring an emergency is a condition of the question, so I will address this at the top without modifying the original part:
An attitude indicator is legally required for IFR flight.  If equipment becomes inoperative during IFR, the pilot should inform ATC.  I do not know that there is any specific legal text that addresses this particular situation you're describing with an ILS approach coupled with an AI failure, but it would be generally accepted by pilots that losing an attitude indicator is an emergency as opposed to losing other required IFR equipment such as the clock.  So, I'm going to go with no, not without declaring an emergency.

Original:
In that situation depending on the circumstances, declaring a missed approach, an emergency informing ATC of the system failure, and requesting vectors to VMC conditions would be the best option.
In an emergency, you can deviate from rules to meet the needs of the emergency at your discretion, so I don't believe that technically you can't still shoot to minimums for the ILS, but it would be dangerous, especially if the pilot isn't highly proficient, and should be a last resort with no primary gyros.
If an approach needed to be shot, and there was no VMC within range, a 'Precision Approach Radar' approach would likely be the best option if one existed within range.  This is can be a 'no-gyro' approach upon request.

I think the real question is "Can you legally (under normal circumstances) fly an ILS approach with the attitude indicator INOP?", which I am sure there is some technical and unambiguous answer to

@J.Hougaard I would think not because of 91.13 regardless of any other rule, but that depends on who you ask. However, that answer is still neither technical nor unambiguous though.

PARs are not necessarily no-gyro -- my understanding is if you want a no-gyro PAR approach, you have to ask ATC specifically for it.  (You can also get a no-gyro ASR/SRA approach, although ASR/SRA is much less precise than a PAR.)

@UnrecognizedFallingObject Thank you for clearing that up!

@UnrecognizedFallingObject obviously, it also depends on the RADAR equipment available

@rbp -- of course -- hard to fly a PAR without the right radar gear for it ;) (I wonder how cheaply one could make an AESA element these days....)

Are there any PAR approaches still available (apart from to aircraft carriers) nowadays?

I'm assuming that we're discussing a flight which departed in an airworthy airplane flying under 14 CFR 91 and a vacuum system failure in IMC has rendered the attitude indicator inoperative.
May the pilot fly an ILS approach to minimums? Yes. There is no regulation requiring that the LOC minimums be used.
May the pilot fly the approach without declaring an emergency? Yes. There is no regulation stating that an emergency must be declared. 14 CFR 91.183 (d), however, requires the pilot to report the failure to ATC as it relates to the safety of flight.

I agree, no emergency need be declared. 14 CFR 91.3(b) makes no requirement for declaring. My school's chief instructor drilled into me that 91.3(b) activates as soon as the PIC thinks "emergency" (or "oh, crap"). 7700/Mayday/declaring are niceties to let ATC know what's going on. Of course, legal and safe aren't always the same thing...


text:
How does the FAA compute the values in TPP's Climb/Descent Table?
The inside back cover of the FAA Terminal Procedures Publication contains a table headed “CLIMB/DESCENT TABLE,” excerpted below.

Source: FAA, p. 19
How do required ascent or descent per nautical mile and ground speed combine to give feet per minute? What is the relationship between the values in the two leftmost columns?

Given a required climb or descent in feet per minute and ground speed in knots, compute the target VSI reading with required climb/descent multiplied by ground speed divided by sixty, or
$$\delta_{VSI} = \frac{\mathrm{RCD} \times \mathrm{GS}}{60}$$
Apply dimensional analysis to see why this works. Informally, we can think of nautical miles and hours in the numerator and denominator as canceling each other out to leave a figure in feet per minute.
$$
\delta_{VSI}\ \frac{\mathrm{ft}}{\mathrm{min}}
=
\mathrm{RCD}\ \frac{\mathrm{ft}}{\mathrm{nm}}
\times
\mathrm{GS}\ \frac{\mathrm{nm}}{\mathrm{hour}}
\times
\frac{\mathrm{1\ hour}}{\mathrm{60\ min}}
$$
Fundamentally, trigonometry determines the values given angles in the leftmost column and the FAA’s definition of a nautical mile being 6,076.1 feet. In a right triangle, tangent is the ratio of the opposite leg to the adjacent leg for a given angle $\theta$, illustrated below for a climb.

For the values in the table

the adjacent leg is exactly 1 nautical mile
the angle $\theta$ is the precise value from the leftmost column
the opposite leg is unknown and is the desired ft/NM value

The core formula is $6,076.1 \tan\theta$ for the ft/NM values, and this is the derivation of the values in the Vertical Path Angle box outlined with a heavy border. Outside this box, the climb rates are rounded to the nearest multiple of 5. The rest of the table values use the $\delta_{VSI}$ formula above.
For reference, see a Google spreadsheet that computes climb/descent rates using the above. The formula for altitude change for a climb or descent at 2.0° over 1 NM is of the form
=mround($O$1*tan(radians(B4)),5)

The value in O1 is the number of feet in one nautical mile. The trigonometric functions in Excel and Google Sheets deal in radians rather than degrees, where a complete circle has $2\pi$ radians.
The formula for the $\delta_{VSI}$ values in feet-per-minute is either
=mround(D$3*$C4/60,5)

or
=D$3*$C6/60

depending on whether the cell is inside the Vertical Path Angle box, i.e., whether the value should be rounded to the nearest multiple of 5 or not.
There are discrepancies, no more than 15 feet per minute. Some of the FAA figures are more conservative, some less. I was not able to discern a pattern; for details, see the color coding in the Computed sheet or the Deltas sheet in the linked workbook. The odd duck is for a 2.0° climb at 210-knot ground speed: the FAA table gives an unrounded value of 743 feet per minute rather than rounding as with its neighbors.
Stack Exchange does not support tables in their Markdown flavor, so a screenshot of the computed table is below.


text:
Is a certificated pilot in a rear seat with no access to flight controls a safety pilot or a passenger?
To be considered a safety pilot, must the aviator in question be able to manipulate the flight controls, or is see-and-avoid responsibility sufficient?
Asked another way, if the PIC wants to fly under simulated instrument conditions to maintain currency in a Cessna 172, is the lone pilot seated in the rear a safety pilot or a passenger? Did the PIC bring along one safety pilot or two?

I think the term "safety pilot" means you need to have access to the controls, not to mention you should have an unrestricted view of the sky to observe and perform the safety duties, which would be difficult from a rear seat. I think the only time this would be acceptable is in a two seat aircraft where you sit in line.

Also, if you are a rated pilot in a passenger seat you should not be logging any time as "pilot" since you don't have access to, or manipulate the controls. I'd hazard to say that even if the rear seat is occupied by a pilot rated passenger, that person is in fact, a passenger, and not performing any duties as a pilot.

@RonBeyer I would be careful trying to make the jump from needing to be a pilot to needing to have access to the controls.  (Note that I agree with your answer below, but your comment above could be taken out of context and give the wrong impression.)

After looking through the FAR's, the answer is no, the rear passenger seat cannot be occupied by somebody claiming to be a "safety pilot".
FAR 91.109(c):

(c) No person may operate a civil aircraft in simulated instrument flight unless—
  (1) The other control seat is occupied by a safety pilot who possesses at least a private pilot certificate with category and class ratings appropriate to the aircraft being flown.
    (2) The safety pilot has adequate vision forward and to each side of the aircraft, or a competent observer in the aircraft adequately supplements the vision of the safety pilot; and

(Emphasis Mine)
So the safety pilot basically has to be able to access the controls and have vision that supplements the pilot, meaning must be able to see as well as the pilot position would.

I find it interesting that while the safety pilot needs to be able to operate the controls, he doesn't actually need to be able to see anything, provided another person does the seeing for him.

@JörgWMittag The language seems to make the competent observer a required crewmember.

Does the competent observer need a medical?


text:
May a non-instrument pilot legally file IFR as long as he amends and doesn’t accept an instrument clearance?
Say a pilot plans to make a cross country flight along Victor airways, but under VFR. Depending on workload and communication effectiveness along the way, our hero may provide the planned fairly complex route to the FAA at least three times.

Flight Service Station
Tower, if departing from such an airport
Approach/Departure Control or ARTCC

This seems like needless frequency congestion. Our hero happens across a suggestion from an ATC specialist that appears to solve the problem for everyone, emphasis in the original.

If you file an IFR flight plan through any system, I will receive it. Make it clear to the first controller you contact that you want to fly your filed route as VFR and give the altitude. It is a very simple amendment I will be happy to make. The only difference on my flight strip is the altitude block that says 60 for IFR or VFR/65 for VFR, and a V in your data block on my radar scope. If you do this, do not accept an IFR clearance. If a controller says cleared to any fix, that is an IFR clearance. Using this method, everything on my end will work smoothly whether you depart a towered or nontowered airport, and this would be the easiest method for the controllers involved. CAVEAT: I do not know if it is legal for a non-IFR rated pilot to file an IFR flight plan even if you don’t accept an IFR clearance.

May a pilot lacking an instrument rating or currency legally do so?

What are you supposed to do if given an IFR clearance? Cancel IFR at that point?

Legality is interpreted by courts, and the NTSB.  See my revised answer.

@DavidSchwartz Simply don't accept the IFR clearance

The FARs say you can't fly an IFR flight plan as a non-instrument-rated pilot. But the rules do allow even non-pilots to file IFR flight plans so that dispatchers and such can do it.

I'd like to take a moment to point out that the required training for the DC SFRA actually instructs for VFR flights to file IFR to trigger the ATC system to generate a discreet transponder code, but VFR flight within the DC SFRA doesn't require an instrument rating. (https://www.faasafety.gov/files/gslac/courses/content/405/1310/200115%20Kneeboard%20-%20Flight%20Plan%20Filing%20Instructions.pdf)

My instrument students, when they get more advanced, file FP with their name, and in remarks say "Training xxxxxx CFII"
That way it is clear.  The FAA office investigated one student, dug up his past flight plans, and determined that the way he filed was acceptable.  The FAA told me they had reports of him going actual prior to his receiving a rating. I gather if the remark wasn't filed, there would have been more questions.
Having said all that, my recommendation is that you file a VFR flight plan for flight following, and then advise ATC upon check-in.  If you are leaving a controlled airport, normally you will advise clearance or ground prior to departure, and then when switching from the tower to departure you will check in with the phrase, "flight following."  On a workload permitting basis you will receive the same handling as IFR flights, in general, and there will be no question as to your intent.
Addendum #1
Just because there is no regulation prohibiting behavior, does not mean that an agency such as the FAA will not prosecute.  In fact, FAA issued a LOI in 2008, on just this topic, stating that if a pilot were to file an IFR flight plan, without holding an IFR pilot certificate, they would consider that intent to violate 61.3.
Now, whether that resulted in certificate action or caused a letter to be filed in your folder, I cannot say, but I would not want my certificate jeopardized by the poor judgment of filing IFR when one was not authorized to conduct IFR operations.
The 2008 LOI comes a decade or so after the incident I reported above with a student.
I don't see how any responsible person can advocate filing a flight plan which is premised upon false and misleading information. Furthermore, while there is not a specific regulation dealing with this particular lack of judgment, the FAA has made clear, with this specific matter, that would consider such a flight plan filing to be a intent to violate 91.3.  Not something that I can see advocating for anyone to do...
Addendum #2

Well that's good to know. I will include my CFI's name on future plans until I get my rating. He'd been having me file to learn the system, and then we fly together or not at all, if it's just for practice.

In this comment, one of our more recent arrivals who's a controller mentions that there's no way for them to pull up a flight plan that's filed as VFR (those go to FSS and no further).  Given the LOI here...there doesn't seem to be a good way to get a flight plan for a VFR operation to be delivered to ATC?

@UnrecognizedFallingObject, flight following appears to permit VFR flight plan callups at least at the local three or four C airspace approach controls.

@mongo -- interesting that that capability wouldn't be available everywhere, or perhaps our fellow poster simply doesn't know of it?

Hi mongo and @Unrec—said recent arrival here. I'm interested in what you mean about "permitting VFR flight plan callups." My suspicion is the radar controller is simply putting you in direct to your destination because they have no way of seeing any more complicated route that you may have filed with FSS. Do you have reason to believe otherwise?

Returning to the LOI... IMHO it shows poor research on the part of the attorneys who wrote it. Notice they coordinated with FSS but not (apparently) with Air Traffic, who would have told them that suggesting the pilot file a "VFR" (FSS) flight plan is completely useless when it comes to assigning a squawk and knowing what their planned route is. Perhaps, in the age of ForeFlight, the regulations could be rewritten to distinguish between "FSS" and "ATC" flight plans, rather than "VFR" and "IFR" flight plans.

How did you find this LOI? I couldn't find it on the FAA website.

I am not aware of, and have not been able to find any regulation governing the filing of flight plans.
The only applicable rule that I know of in the FAR's is 14 CFR 61.3(e), which says that no pilot may act as PIC under IFR (which you would not be doing in the situation that you describe above):

(e) Instrument rating. No person may act as pilot in command of a
  civil aircraft under IFR or in weather conditions less than the
  minimums prescribed for VFR flight unless that person holds:
(1) The appropriate aircraft category, class, type (if required), and
  instrument rating on that person's pilot certificate for any airplane,
  helicopter, or powered-lift being flown;
(2) An airline transport pilot certificate with the appropriate
  aircraft category, class, and type rating (if required) for the
  aircraft being flown;
(3) For a glider, a pilot certificate with a glider category rating
  and an airplane instrument rating; or
(4) For an airship, a commercial pilot certificate with a
  lighter-than-air category rating and airship class rating.

I do remember my instructor having me file IFR flight plans when I was working on my instrument rating (with them as the PIC), and for that matter many airlines and flight planning services often file flight plans on behalf of a pilot.  I doubt that all of them have instrument ratings (many aren't even pilots) yet it happens all of the time and I can't find any examples of violations.

EDIT:
As @mongo provides in his answer, the FAA has issued an LOI on this matter, and while my answer stands as far as the legality of having non-certificated people file flight plans, they feel that it would be against the rules to list a non-qualified pilot as the PIC.  Therefore, if you are filing on behalf of someone else who is qualified, all should be well, but don't do it if the PIC is not instrument rated.

The question is not really about second or third party persons filing flight plans. Rather it is about a pilot, filing an IFR flight plan, perhaps with the intent of cancelling it, but filing it for himself, and with himself as the pilot of record on the flight plan.  The FAA has interpreted that action as something they might seek enforcement on, and therefore it is ill advised.

@Mongo What are you trying to say? I mention that in my answer, and even commented on yours saying that you made it clear with your reference....  The way that the question is worded, people may still end up here and find the additional information useful, but again, everything that I said agrees with you.

The last two sentences of the OP posting made it clear that the pilot filing would be the pilot flying, and that they lacked a rating or currency. The last sentence of your last two paragraphs deal with the filer, and the real issue is who is the flier. The answer should address the concern of the OP, not a variant which could be confused with the question being asked.

@mongo Nothing which I said contradicts what you just said....  The last two sentences say "I do not know if it is legal for a non-IFR rated pilot to file an IFR flight plan even if you don’t accept an IFR clearance.
May a pilot lacking an instrument rating or currency legally do so?" I answered that question, as well as the question of whether the PIC needs to be instrumented rated while referencing your answer since you found the LOI.

Comment to you and @mongo. The Goodish LOI emphatically does not say that the FAA considers it against the rules to list a non-qualified person as PIC. Rather they consider it against the rules for a non-qualified person to act as PIC. Filing an IFR flight plan does, as the Goodish letter points out, signify intent to break the rule. But filing the flight plan is not in and of itself a violation.

@randomhead The FAA has made it clear that they may pursue certificate action based upon intent.  My suggestion was to include a CFII name, etc. to make clear the filer's intent.  Please see addendum #1 in my answer above.

@mongo do you have a reference for the FAA pursuing certificate action based on intent without an actual violation of the CFRs? For example, 91.17(a) says that a person may not "act or attempt to act as a crewmember" if they are under the influence. But 61.3(e) does not prohibit intending to act as PIC without the proper ratings; a violation only occurs if someone actually does act as PIC.

@randomhead my original work on this issue came about over 20 years ago, when an instrument student was being investigated for flying IFR lacking a rating.  The FSDO investigated, and interviewed me as part of the process.  Based upon my records, and the evidence provided by some party to the FAA, the operations inspector investigating decided to not pursue the matter further.  Later, in 2008, the attached LOI was issued by the FAA.  The FAA has invoked enforcement based upon actions of pilots. Violations are determined by NTSB and courts, and are, unless sealed, public record.


text:
Is the life of pets considered when dealing with a cargo fire indication?
In this event, the crew of a 777 responded to a spurious cargo fire indication by activating the fire suppression system, which suffocates the cargo area. Presumably any pets held there would have died as a result.
What are the SOPs for fire suppression when carrying pets in the cargo hold? Are they held in a separate compartment?

Don't think there is one. And to be brutally honest, as much as those who love their pets will disagree: The value of an animal compared to hundreds of humans will always be less, so in the event of a fire, the suppression system will be triggered. According to this blog, carrying pets in the cargo hold should be a last resort thing.

After a bit of further research, there seems to be the option of discharging a slightly different agent for cases where animals or perishable goods are transported. See also this PDF.

Not sure if the above sources warrant a complete answer though.

Our 2 dogs flew in pressurized cargo from JFK to TLV back in the early 80s. As much as I loved those dogs, I'd much rather them die from fire suppression in the hold than have the entire plane go down. Had the added bonus of watching them change a flat on the 747 prior to departing TLV for the return trip while we walked the dogs and waited!

Cargo fire is the worst kind of fire and is easily capable of bringing down the whole plane unlike an engine fire. If EICAS indicates a fire back there I'm blowing the bottles and landing at the nearest suitable. Pets are not a consideration over the human souls on board.

As a matter of historical trivia, 727-100s had a aft lower cargo hold that was normally heated, and that was where pets were often carried.There was a switch on the f.e. panel that controlled whether or not it was heated. The switch was colloquially referred to as the "dog killer switch."

If there's a fire in the cargo hold, wouldn't any animals in the hold most likely die regardless of whether or not the halon was used?

What happens to live animals in cargo depends on the type of airplane and the class of cargo compartment they're traveling in. For a typical passenger airliner, if you check your animal as baggage, they're going into the "lower lobe cargo compartment" under the cabin floor. This is classified as a Class C compartment, which essentially means that the crew have no access to it in flight, so it must contain fire detection and extinguishing systems. The applicable regulation is 14 CFR 25.857.
Quite simply, there are no considerations for live animals in Class C compartments. If you look in Boeing cargo fire checklists (copyrighted so can't post here, but you might get lucky with Google), the steps in the checklist deal with discharging the Halon into the cargo compartment and adjusting the pressurization system to minimize flow into the cargo compartment. This helps maintain the minimum required Halon concentration to provide the first big knockdown blast to stop the fire from spreading, and then maintain a low-level concentration to keep it suppressed for the length of the diversion to a landing. Unfortunately, that means any live animals will suffocate since Halon displaces oxygen.
For dedicated freighters such as the 747-400F/747-8F/777F etc., the main deck area is considered a Class E cargo compartment, which doesn't have a fire extinguishing system. If a fire is detected here, the procedure is to depressurize the entire cabin and minimize/cutoff air flow to the main deck area, and climb/descend to a mid-altitude (somewhere in the 24,000-28,000' range depending on the airplane) to minimize oxygen and help suppress the fire. If animals are transported here, rather than the Class C lower lobe compartments, they may survive. They may become hypoxic and lose consciousness, but there's no Halon to suffocate them. Depending on the length of time for the diversion to safe landing site, the lack of oxygen may be a serious issue for some animals just as it can be for humans, but that's a guess as I'm not a vet.
Bottom line is if you're taking your pet with you on a commercial flight, the safest, most comfortable, and least traumatic place for them is with you as a carry-on item.

I worked in IT in the '80s, and computer rooms were routinely protected with Halon. We were taught that Halon was relatively safe. A number of my colleagues were in the computer room when it was accidentally  dumped into a room with at least 6 people working in it. They were all fine. IIRC, we used a concentration of 7% Halon 1301, which cannot displace all the oxygen. Halon works by interfering with the chemical reaction that is fire,

As said in the other comment, only a low concentration of halon is needed to extinguish a fire. This is because it inhibits the chemical reactions during combustion, while there is plenty of oxygen around. That's great, since humans and animals can still breathe that air. BUT: there is still the smoke in the air, and the stuff produced by the halon in the fire is also nasty. That means, an animal will not die due to the lack of oxygen, but may be due to the gases from the combustion.


text:
What is minimal altitude that aircraft (rocket?) can fly above any country without any permission?
What is minimal altitude that aircraft (rocket?) can fly above any country without any permission? I mean, at what altitude ends country's airspace?

I cannot answer properly, but I think it will depend if the device (might not be an airplane?) is armed or not.

@TrebiaProject. I thought it does not matter. But if it is important let's suppose that it is military device and it is armed.

according to space treaties you should not have any weapon there, so it will be restricted to the area between what we call apace and the country limit

@what about military spy (not armed) device?

the only thing I know for sure is the mass destruction weapons cannot be in space... difficult to make the difference between weapon and some systems

Historically, the ceiling of the other team's interceptors or AA missiles.

@BrianDrummond Now you can shot satellite with missile launched from plane or ship. I think nowadays that rule does not applies.

A domestic aircraft or a foreign aircraft crossing political borders?

Actually, what you're asking are two different questions- According to ICAO ( ICAO Annex 11: Air Traffic Services), Class G airspace is uncontrolled and aircraft can fly in the without ATC permission. The definition if Class G is left to the regulatory authorities of individual countries (in US, it is where the other airspace classes are undefined).
Where does the airspace of the country end is a completely different one and as of now, there is no agreed definition. The United Nations General Assembly Committe on Peaceful Uses of Outer space is still in the process of defining what exactly an outer space is.

What is minimal altitude that aircraft (rocket?) can fly above any country without any permission?

100 km, probably

the Kármán line, at an altitude of 100 km (62 mi) above sea level,[7][8] is conventionally used as the start of outer space in space treaties and for aerospace records keeping. The framework for international space law was established by the Outer Space Treaty, which was passed by the United Nations in 1967. This treaty precludes any claims of national sovereignty and permits all states to freely explore outer space.

- Wikipedia

It depends on the country's level of aggression and anti-aircraft weapons. The U2 made several flights over the USSR at 70,000 feet without permission. Governments will always claim as much territory as they can get away with diplomatically and militarily.
The ability to orbit is a practical limit, there is a zone where aircraft don't have enough air to maneuver yet there is enough air to quickly slow orbiting spacecraft.
The airspace up into this zone is pretty well defended by large countries in the modern era, while small countries may not respond to relatively low flights.

As per Wikipedia there is no internationally agreed upper boundary of national airspace, but if there was it would be up to the countries themselves. Some equatorial countries tried to define their airspace up to the geostationary orbit altitude at 35,786 kilometres (22,236 miles) - see the 1976 Bogota Declaration:

The Declaration of the First Meeting of Equatorial Countries, also known as the Bogota Declaration, is a declaration made and signed in 1976 by eight equatorial countries, and was an attempt to assert sovereignty over those portions of the geostationary orbit that continuously lie over the signatory nations' territory. These claims have been one of the few attempts to challenge the 1967 Outer Space Treaty, but they did not receive wider international support or recognition. Subsequently, they were largely abandoned.

The United States' FAA legislation ends at the upper boundary of class A airspace at 60,000 ft (18.3 km). Additionally, the FAA defines a space border at 264,000 ft (50 mi / 80.5 km).

Class A is from 18,000 feet above sea level to FL600. The FAA classifies all airspace above FL600 as Class E, the same as most of the airspace below 18,000 feet.


text:
Was John F. Kennedy Jr.’s accident airplane equipped with an autopilot?
JFK Jr.’s crash was attributed to failure to maintain control due to spatial disorientation. Could this be explained by his Piper Saratoga N9253N having no autopilot?

According to the NTSB, the accident airplane did have a functioning autopilot and GPS.

The airplane was equipped with a Bendix/King 150 Series Automatic Flight Control System (AFCS), which was approved for use in Piper PA-32R-301 model airplanes by the FAA on November 1, 1982. The AFCS provided two-axis control for pitch and roll. It also had an electric pitch trim system, which provided autotrim during autopilot operation and manual electric trim for the pilot during manual operation.
The AFCS installed on the accident airplane had an altitude hold mode that, when selected, allowed the airplane to maintain the altitude that it had when the altitude hold was selected. The AFCS did not have the option of allowing the pilot to preselect an altitude so that the autopilot could fly to and maintain the preselected altitude as it climbed or descended from another altitude. The AFCS had a vertical trim rocker switch installed so that the pilot could change the airplane's pitch up or down without disconnecting the autopilot. The rocker switch allowed the pilot to make small corrections in the selected altitude while in the altitude hold mode or allowed the pitch attitude to be adjusted at a rate of about 0.9 degree per second when not in altitude hold mode.

According to the same report, at least two different CFIs judged the accident pilot at least adequate in the operation of the airplane’s autopilot.

A second CFI flew with [Kennedy] between May 1998 and July 1999. This CFI accumulated 39 hours of flight time with the pilot, including 21 hours of night flight and 0.9 hour flown in instrument meteorological conditions (IMC). The pilot used this CFI for instruction on cross-country flights and as a safety pilot. On July 1, 1999, the CFI flew with the pilot in the accident airplane to MVY. The flight was conducted at night, and IMC prevailed at the airport. The CFI stated that, during the flight, the pilot used and seemed competent with the autopilot.

Also:

A third CFI flew with the pilot between May 1998 and July 1999. This CFI accumulated 57 hours of flight time with the pilot, including 17 hours of night flight and 8 hours flown in IMC. The pilot also used this instructor for instruction on cross-country flights and as a safety pilot. This CFI had conducted a “complex airplane” evaluation on the pilot and signed him off in the accident airplane in May 1999. According to the CFI, on one or two occasions, the airplane’s autopilot turned to a heading other than the one selected, which required the autopilot to be disengaged and then reengaged. He stated that it seemed as if the autopilot had independently changed from one navigation mode to another. He also stated that he did not feel that the problem was significant because it only happened once or twice.

53N’s GPS was capable of driving the autopilot.

The accident airplane was equipped with a GPS receiver, Bendix/King model KLN-90B. The GPS was capable of presenting moving map displays; bearings and distances to programmable destinations, such as airports and waypoints; airport information; ground speed; and other information. The GPS was also capable of interfacing with the AFCS and the pictorial navigation indicator.

The accident occurred in July 1999. The KLN-90B’s navigation database was not current.

The navigation database indicated that it was effective on October 8, 1998, and that it expired on November 4, 1998.

As to operability

On July 29 and 30, 1999, the avionics were examined at the AlliedSignal/King Radios Facility, Olathe, Kansas, under the supervision of a Safety Board investigator. On October 13 and 14, 1999, a follow-up examination of the navigation and communications transceivers and all three autopilot servos was also performed at the AlliedSignal/King Radios Facility under the supervision of a Safety Board investigator. [P]arties to the investigation were present during both examinations.
The accident airplane’s AFCS was examined. Examination and functional testing of the AFCS pitch, pitch trim, and roll servos did not reveal any evidence of a preimpact malfunction or jam.

I co-own a KFC-150/KAP-150.  I think it’s important to note that unlike some more recent autopilots with robust envelope protection, or advanced recovery modes like the GFC500 “LVL” button, the KFC 150 will not do a good job of getting you out of trouble once you are already in trouble.  I have to be within a fairly limited flight envelope to engage the 150, and it will keep me there.  But I can’t engage it after I am in trouble.  He would have needed to engage the autopilot before getting disoriented, as it’s not designed to rescue you from an unusual attitude.

When Cirrus introduced its Perspective IFD System, a proprietary version of the Garmin G1000 IFD, for its SR2X line of aircraft, a joke term amongst Cirrus reps in the northeast was to refer to the blue LVL button on the GFC700 autopilot as “The JFK Jr. Button”.  I dunno if this or the CAPS would have saved those 3 souls on the night of 16 July, 1999, but that was the claim.